Implantable neurostimulator devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable neurostimulator.
As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible device case 30 formed of a conductive material such as titanium for example. The case 30 typically holds the circuitry and battery 26 necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 includes one or more electrode arrays (two such arrays 102 and 104 are shown), each containing several electrodes 106. The electrodes 106 are carried on a flexible body 108, which also houses the individual electrode leads 112 and 114 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on array 102, labeled E1-E8, and eight electrodes on array 104, labeled E9-E16, although the number of arrays and electrodes is application specific and therefore can vary. The arrays 102, 104 couple to the IPG 100 using lead connectors 38a and 38b, which are fixed in a non-conductive header material 36, which can comprise an epoxy for example.
As shown in FIG. 2, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils (more generally, antennas) are generally present in the IPG 100: a telemetry coil 13 used to transmit/receive data to/from an external controller 12; and a charging coil 18 for charging or recharging the IPG's battery 26 using an external charger 50. The telemetry coil 13 is typically mounted within the header 36 of the IPG 100 as shown, and may be wrapped around a ferrite core 13'.
As just noted, an external controller 12, such as a hand-held programmer or a clinician's programmer, is used to wirelessly send data to and receive data from the IPG 100. For example, the external controller 12 can send programming data to the IPG 100 to dictate the therapy the IPG 100 will provide to the patient. Also, the external controller 12 can act as a receiver of data from the IPG 100, such as various data reporting on the IPG's status. The external controller 12, like the IPG 100, also contains a PCB 70 on which electronic components 72 are placed to control operation of the external controller 12. A user interface 74 similar to that used for a computer, cell phone, or other hand held electronic device, and including touchable buttons and a display for example, allows a patient or clinician to operate the external controller 12. The communication of data to and from the external controller 12 is enabled by a coil (antenna) 17.
The external charger 50, also typically a hand-held device, is used to wirelessly convey power to the IPG 100, which power can be used to recharge the IPG's battery 26. The transfer of power from the external charger 50 is enabled by a coil (antenna) 17'. The external charger 50 is depicted as having a similar construction to the external controller 12, but in reality they will differ in accordance with their functionalities as one skilled in the art will appreciate.
Wireless data telemetry and power transfer between the external devices 12 and 50 and the IPG 100 takes place via inductive coupling, and specifically magnetic inductive coupling. To implement such functionality, both the IPG 100 and the external devices 12 and 50 have coils which act together as a pair. In case of the external controller 12, the relevant pair of coils comprises coil 17 from the controller and coil 13 from the IPG 100. In case of the external charger 50, the relevant pair of coils comprises coil 17' from the charger and coil 18 from the IPG 100. As is well known, inductive transmission of data or power can occur transcutaneously, i.e., through the patient's tissue 25, making it particularly useful in a medical implantable device system. During the transmission of data or power, the coils 17 and 13, or 17' and 18, preferably lie in planes that are parallel, along collinear axes, and with the coils as close as possible to each other. Such an orientation between the coils 17 and 13 will generally improve the coupling between them, but deviation from ideal orientations can still result in suitably reliable data or power transfer.
The concurrent application incorporated above—with which the reader is assumed familiar, and which is not fully discussed here—discloses an improved architecture for an IPG 295 as shown in FIGS. 3A and 3B. The improved IPG architecture involves integration of various IPG functional circuit blocks (FIG. 3B) on a single integrated circuit (IC) 300 via a bus 297 governed by a communication protocol. To communicate with the bus 297 and to adhere to the protocol, each circuit block includes bus interface circuitry 215 (FIG. 3B) adherent with that protocol. Because each circuit block complies with the protocol, any given circuit block can easily be modified or upgraded without affecting the design of the other blocks, facilitating debugging and upgrading of the IPG system 290. Moreover, because the centralized bus 297 can be taken off the integrated circuit 300, extra circuitry can easily be added off chip to modify or add functionality to the IPG 295.
For example, and as shown in FIG. 3A, two electrode driver ICs 300 and 300' are daisy chained to double the electrode capacity in the IPG 295, i.e., from 16 to 32 electrodes as shown. ICs 300 acts as a master while IC 300' acts as its slave, with discrimination between the two being enabled by chip select signals CS_m and CS_s respectively. Microcontroller 305 provides for control of functions in the system 290 not handled by various circuit blocks in the ICs 300 and 300', and otherwise generally acts as the system's master. However, it is not necessary that ICs 300 be daisy chained pursuant to the strategies disclosed in the concurrent application, and instead an IPG system may use only one such IC 300.
Referring to FIG. 3B, each of the circuit blocks in IC 300 performs a particular function in an IPG. For example, telemetry block 62 couples to the IPG telemetry coil 13, and includes transceiver circuitry for communicating with the external controller 12 (FIG. 2). The charging/protection block 64 couples to the IPG charging coil 18, and contains circuitry for rectifying power received from the external charger 50 (FIG. 2), and for charging the power source (battery) 26 in a controlled fashion. Stimulation circuit block 175 is coupled to the electrodes E1-E16 and includes circuitry for setting the program (magnitude, and polarity) for the stimulation pulses appearing at those electrodes. Stimulation circuit block 175 also includes the drivers for the electrodes, with a Digital-to-Analog Converter (DAC) 82 being responsive to the stimulation program to supply current to the specified electrodes via current source and sink circuitry. Notice that the electrodes E1-E16 are connected to off-chip decoupling capacitors C1-CN prior to connection to the corresponding electrodes 106 on the leads 102 and 104 (FIG. 1A); such decoupling capacitors C1-CN prevents direct DC current injection from the IPG into the patient, which is advisable for safety, but otherwise such decoupling capacitors do not significantly affect stimulation performance.
The compliance voltage (V+) generator block 320 generates a compliance voltage, V+, which is used by the current sources (DAC 82) in the stimulation circuitry block 175. The clock generator block 330 generates the communications clocks to synchronize communications on the bus 297, as well other clocks needed internal to the IC 300. The master/slave (M/S) controller 350 informs the IC 300 whether it is acting in a master or slave capacity should the IC 300 be operating in a system with more than one IC 300, such as is shown in FIG. 3A. Interrupt controller block 173 receives various interrupts from other circuit blocks, which because of their immediate importance are received independent of the bus 297. Internal controller 160 acts as the master controller for all other circuit blocks. EPROM block 177 caches any relevant data in the system (such as log data), and additional memory 66 can also be provided off-chip via a serial interface block 167. External terminals 202 (e.g., pins, bond pads, solder bumps, etc.) are used to carry signals to and from the IC 300.
Of particular relevance to this disclosure are the sample and hold block 310 and the Analog-to-Digital (A/D) block 74. As shown in FIG. 3B, the sample and hold block 310 receives various analog signals via an analog bus 192, such as the voltages appearing at the electrodes E1-E16, the battery voltage (Vbat), the compliance voltage (V+), etc. The goal of the sample and hold block 310—as its name suggests—is to sample selected ones of the various analog bus 192 signals, and to hold then so their voltage magnitudes can be resolved. The resolved analog voltages are then sent from the sample and hold block 310 to the A/D block 74 where they are digitized and sent for interpretation via the bus 297 elsewhere in the IC 300 or microcontroller 305.
It is particularly important to monitor the voltages at the electrodes, either during stimulation or testing. Assessing such voltages is beneficial for many reasons. Knowing the electrode voltages allows the resistance between the electrodes, R, to be calculated, which is useful for a variety of reasons. Also, knowing the voltages present at the electrodes during stimulation can be useful in setting the compliance voltage, V+, at the V+ generator 320 (FIG. 4B) to an appropriate and power-efficient magnitude. See, e.g., U.S. Pat. No. 7,444,181. This disclosure presents improved sample and hold circuitry for the sample and hold block 310 for assessing electrode and other voltages of interest in the IPG.